Installing solid tires without locking pins?
A seller of airless tires in 2013 demonstrates how to install his product onto a (spokeless) rim, pushing it in place, using a zip tie cinched tight to hold it for starters as he progressively levers the tire over the rim flange with a large, plastic prying spatula, finally kneading it all round, inch by inch, to seat the tyre.

This writer suggests it may go easier if the tire is warmed up. Cursing may do the trick.