First, only mom feeds the baby (both solids and bottles). Baby is always held by mom when being fed.
Don’t allow baby to hold his own bottle. If baby is used to holding his own bottle you may need to gradually get him used to you holding it. Put a sock over it so that it looks more like a piece of clothing than a bottle.
When baby is comfortable with mom holding the bottle, and being held by mom while feeding you are ready to try the at breast supplementer (abs).
The first step is to thread the tube of the abs through the nipple he usually takes, and feed him that way (you can use a tapestry needle to thread supplementer tube into the nipple. it only needs to stick out a little).
Next, move the bottle nipple over your own nipple.
Once he is comfortable sucking on the nipple with the abs over your nipple you are ready to try and move him to your breast. Toward the end of the feeding try and switch him to your breast.
You may try to feed at first with the abs (even if you have a good supply) as baby may like the faster flow he is used to getting from the bottle. You can eventually wean off of the abs (usually very quickly if you have a good supply).