I am presuming that this foot and your sofa uses standard size 5/16 inch holes. For most sofas, you need to buy a 5/16 inch x 3 inch hanger bolt for each leg. Sometimes you can use a shorter hanger bolt, but I recommend 3 inch, since shorter hanger bolts sometimes don't work. Hanger bolts are half screw and half bolt.. The screw end goes into the wooden furniture foot so that you can screw the bolt end into the sofa.
To insert the screw end into wooden foot, you will need a couple wrenches or pliers and a couple 5/16 inch bolts as explained next. First put two 5/16 inch nuts next to each other near the top of the bolt end. They will lock together when you turn the outer bolt with a wrench, allowing you to twist the screw end into the large hole at the top of the wooden foot. The screw will stop turning when the bolt part starts to enter the wooden foot. You will need a second pliers or wrench to "unlock" /separate the nuts and take them off so you can reuse them to insert the next hanger bolt in the next foot..
Normally, the holes are deep enough, but if you have trouble putting in the screw all the way, you can drill the hole deeper with a 5/16 inch drill bit. Hanger bolts are removed from wooden feet using the same double-nut method to grab and turn the bolt. However, you turn the inside nut instead of the outside nut.