Firstly I'm assuming you meant a - inplace of the equals sign in the brackets. Also, naturally, I'll assume that , and are all constants.
To do this you simply use the substitution where to transform the equation in terms of , the function and its derivatives wrt . So to start you off you should find that
and, using Leibniz's differentiation of products rule),
Further to this you only need to substitute for the derivatives of wrt using:
Assuming your original equation was correct this should do the trick transforming it into the Bessel equation. Hope that helped!