Circuit restoration is not for the fainthearted so I hope you know what you’re letting yourself in for as usually it ends up being a labour of love and costs more in time (and sometimes parts) than is sometimes warranted.
You don’t state what parts are missing so here’s the schematic for the amplifier that should help.
It shows the compete circuit with component type and values so you may just have to start tracing through the amp, using the circuit to where the “missing” parts are and find out what type and value component they are (were?) as per the circuit diagram and then search on places such as digikey.com or mouser.com to find replacements. If you are unlucky and the component is “proprietary” e.g. the power transformer then this makes it more difficult because it may no longer be available and you have to contrive using the nearest suitable replacement.
After you have replaced all the missing parts then you need to check if it works as chances are that it won’t. Ask yourself why were there parts missing in the first place? Have they been removed because someone else tried to fix it and gave up or used the amp as a “donor parts” amp to fix another one perhaps?
After checking that the power transformer is OK i.e. not short circuit, open circuit or short to earth (if the original is still there that is and not a new replacement that you installed) and that you’re not likely to blow the fuse straightaway, you can apply power to the amp for the first time.
Be prepared to remove the power immediately if some components start to get hot very quickly and they start to smoke.
If nothing at all happens when the power is connected and the amp is turned on, then at least you have the schematic to find out why it is not powering on.
I’m certainly not trying to discourage you from doing this, just letting you know what may be in store for you.
Have fun ;-)