If you break the plastic foot rest, Medline wants you to replace both the plastic part and the metal part it is fastened to.  In fact, you can only by them in pairs, so you end up spending a lot more than you should.  For example, the whole chair, new, runs about $240 on the Medline at home website, while the pair of replacement footrests runs about $60 (US).

This model is my replacement for the original part.  It isn't an exact match, but it serves the same function.

In the pictures, the black foot rest is the broken one.  I tried to glue it back together, but it didn't hold.  The red foot rest is the replacement part printed flat on the bed with tree supports from the printing surface only to support the interior of the curved section.  I made mine out of PETG for heat resistance.

Replacement (fits either left or right side) foot rest for the Medline Combo Rollator/Transport Chair model MDS808200TR.