Try beans, milk, or hot sauce/seasoning from a restaurant (you may buy some from the store, but it won’t work as well in my experience). These all tend to loosen your stool to various degrees.

However, to be frank, the constipated stool will still be hard; all this will do is cause new stool to put pressure on old stool. This constipated still may still be hard to pass, although those foods should help.

Edit: Pears work too