@vv Ok, but the problem is that I don't know the function f(s) and don't want to solve the integral. I just need to formulate one integro-differential equation and, to do so, I need a change of variables. Supose, as an example, a different case:

Change(int((diff(f(s), s))^2, s = L .. s), s = S*L, S)

the same error occurs:

Error, (in IntegrationTools:-Change) unable to determine new range for S