I don't think this is the best venue to ask the question you are asking but since you ask:

I do Viking Age reenactment so I will be talking about it in that context but there is also a lot of continuity in practices so I assume some of it translated.

Drawstring pouches (like the Hedeby pouch) typically hung on garter belts under the tunic thus to hide valuables from thieves but it is possible they could be hung on the outer belt as well. Although a lot of the wealth was worn on the person in the form of jewelry (like arm bands) coins and pieces of hack silver were stored in those pouches.

While we know they had pouches, there isn't really a known tying method that has been found for the period. There isn't really indication that I know of from grave finds as the items that would lead to those clues rotted away and illuminated images I have seen are not very helpful as most pouches appear to use the top-flap over the belt to hold it to the person (like one of the dudes here) or had a strap like a purse (like this) even though draw pouches are known to exist.

So how should you affix it to your person? Since you use it to keep things you want to retrieve easily you should keep it on your outer belt but the right way would be on the garter belt for holding up your trousers or hose for both men and women. To affix it to your garter belt, the easiest method is to hoop it on the belt like this (It's not a pouch but it uses the same idea) Thus you are not having to tie and unknot your pouch every time you want to get into it and thus will make the drawstring last longer.

EDIT: It might be easier for the meathod I stated if the drawstring is not too thin, if so try to replace it with thicer cord.