If you recall where you got these chairs, contact them and ask. Another option is call your local home center and ask, or take the chair there.

You'll need a pro to do it right.

If you want suggestions for DIY, that I can do: Glue down or remove any/all the splinters sticking out and repaint them.

Drill it out and run a smooth head stainless steel bolt through with washers and lock washers. Easy.

Thanks all 👍.

Is that vertical framing with the rectangle hole between a pair of two round bolt holes plastic or metal?

Any repair would need to be able to hold the weight of any person or pet sitting on it.

Per "Joseph Corlett, LLC.... if those "bolts" are metal, do "Drill it out and run a smooth head stainless steel bolt through with washers and lock washers".

There could be liability issues if the chair collapsed and someone were to be injured so, if those pieces are plastic and/or you want additional support: ...

IF the vertical frame with the rectangle hole has strength, then you may be able to put use a treated board inserted into that rectangle on each side and then connect the side/arms/legs to each end of that board with screws (through framing if at all possible), adding washers both inside and outside the "fabric" side arms/legs so that outer woven material doesn't tear.