For all Ps1 Modchip Installation Instructions I'd Highly recommend checking out the Following Site
They have very solid diagrams for MM3 and Mayumi modchip installations
If you're more interested in installing a PSIO ODE device in your Ps1, then check out the installation diagrams here.
I do offer a send in service for PSIO on the shop if you don't feel up to the task!
PSIO Installation Video