If you can smell something before you make the bracha and check if you can smell something, and you will be able to smell afterwards hen you could make the bracha on the Besamim. If you are uncertain whether you can smell it, then you may still make the bracha for you family so they can smell it.
Explanation:
The Gemara Brachot 53b: Rav Yehuda said in the name of Rav we don’t go run to look for a Havdalah flame the way we usually chase after Mitzvot. R’ Zeira said I used to search but then I heard what Rav Yehuda said in the name of Rav I also stopped looking but if I have it, I will make a bracha.
We see that there is no obligation to look for fire on Motz” Sh but if you have it you make a bracha. The Rashba in the name of the Raavad says similarly Besamim one does to have search everywhere to get some since it is a bracha for oneself and if you do not want to enjoy smelling spices then you do not have to make a bracha.
The Drisha writes that Besamim are to calm a pained soul at the departure of Shabbat. We can’t force someone to un around looking ofr Besamim to calm himself down.
The Shulchan Aruch (297:1) rules: One makes a bracha on Besamim if he has and if he doesn’t, he does not have ask round for some.
The Chazon Ish stressed, though, that if one has Besamim handy then he must make a bracha and smell them.
It is apparent that smelling Besamim Motzei Shabbat is somewhat optional.
Since it is only a good custom that Rabbeinu Efraim said that if one cannot smell and make a bracha no the Besamim it is a wasted bracha, nor can he make the bracha for his household to smell unlike Kiddush Havdalah , which are obligations, but this is only a good custom.
The Rosh asked, the Gemara in Rosh Hashanah 29b says: The rabbis taught one should not make a bracha for guests unless you are eating with them, but you may make a bracha for your kids to teach them. It seems that it’s permitted to make a bracha for the family even if you are not thing. The Bet Yosef answers that the Gemara in Rosh Hashanah is when the kids are little but with adult children someone who is not eating can not make a bracha for them.
This machloket applies by all Brachot on pleasures if one may say the bracha for someone else, and it applies by Havdalah Besamim as well, even if he can’t smell he might be able to.
The Bet Yosef argues that Havdalah Besamim are not just for pleasure rather the bracha is part of Havdalah as set by the Chachamim therefore its similar to Kiddush and Havdalah.
Therefore, in Shulchan Aruch 297:5 he rules: he who cannot smell should not say a bracha on the Besamim unless he makes the bracha for young children or for those who cannot make the bracha for themselves.
The are many Poskim who argue on the psak of the Shulchan Aruch , the Taz Magen Avraham, who are afraid to rule against Rabbeinu Efraim that one who can’t smell cannot make a brachah for others.
So writes R’ OY one who can’t smell is exempt from Birkat Besamim. And he may not make the bracha unless he has small children in the house and he needs to teach them.
In our case where he can smell sometimes so he should open the Besamim and if he smells a little bit then he should say a bracha and smell it again. As the Kaf Hachaim says (216:3): If one is in doubt whether the grass has a smell, he may test it before and then make a bracha… However, if you may smell sometimes one may check before eh make as a bracha. If he can’t then the Kaf Hachaim says he may make a bracha and have in mind to Motzi the other family members since he usually can smell and now it is in doubt, he may follow the Rosh and Motzi others.
