Generally here's how it's gonna go down.
1) you will have to use GECK. prepare yourself if you're one of those modding-tools shy people. Apply lube liberally. (but honestly it's not that bad). Get Nifskope as well.
2) since you dont seem to be too experienced your best bet is 'copy-pasting' assets from existing mods into the ruger.
3) follow this tut: https://www.youtube.com/watch?v=1jRhO3Lvf7U. Basically you have to select the weapon scope / sight part, right click, "copy block" and paste it into the "BSFadeNode" on the very TOP of the block list (the list with all the stuff on the left of the nifskope window). right click on the "BSFadeNode" entry, do "paste block", then edit the newly pasted block- give it a unique name and so on and so forth.
3) if you want an EOTECH it'll probably have another 'lens' mesh for the holographic sight inside. you'll have to adjust the sighting nodes to line up with the crosshairs in the EOTECH lens.
there's a tutorial I saw on the GECK wiki for this exact situation, but I can't seem to find it again for the life of me.