My online skates are broke

Here is what I would do. Pretty quick and dirty solution and I am sure this can be improved upon but it should get you going.

Remove the large rivet (Should come of by grinding the back down with something like a Dremel tool or you can also drill it out).

Get a piece of sheet metal (not sure where you are located but our local Hardware stores all have small sheets for sale.) Get something like a 18 or 20 gauge thick. Not thinner. Cut it to a size which approximately measures what the old plastic tab was. Use a small hammer and vise (or similar and bend the sheetmetal just slightly in the shape of the plastic ridge. May take a bit of practice but should really not be to complicated.

Now attached the formed piece of sheetmetal to the left over plastic tab on the left side with some pop rivets (blind rivets). for that you need to drill two hole through the sheetmetal and the plastic. Temporarily hold the sheetmetal tightly in place to the plastic by using some vise grips (locking pliers). Drill the holes. Get some deep pop rivets (something like 1/8” rivets 1/2 or 3/4 depth.

Push the rivets in place but use some washers in the back part. That will avoid pulling the rivets through the plastic. If this point is vague, let me know and I will add an image of what I have in mind (once I get off work of course ;). Now with the metal attached to the plastic, pull the metal and plastic to the right side (1). Nice and snug. Keep it secured in place by attaching some locking device like either vise grips or even a small c-clamp etc. in area (2) Once it is secured, mark the area where the center hole for the large rivet is. It is best to mark it from the inside of the skate to the outside. When you have it marked, you can undo the C-clamp or whatever you used to secure the two piece. Drill the hole in the marked area for the large rivet.

Once done, reassemble everything right up to the point where you pull the sheet metal/plastic side very snug and line up the hole for the Rivet. You will now have to reapply a rivet and that is where I can not help. You will have to measure that rivet when you originally remove it, Go to your hardware store or even an online store and find a good replacement. Those rivets are not hard to install and do not require any major special tools etc. That in a nutshell should be it. Like I said, I am sure this can be improved on but it should at least get you going .