Canon 500mm F4.0 IS L USM Mk1 lens screws

Hi All,

I have a 500mm f4.0 lens which I need to fix as it is no longer serviceable by Canon or their representatives.

I want to find out what screwdriver or allen-key needs to be used to remove the very small screws on the front ring as I do not want to damage these screws. (see extract from manual to understand what screws they are)

Thanks in advance for any help