Who can scan old photo slides (they’re already developed) or can tell me how to do it myself? I think each slide is 35mm.
How many do you have to process?
There are services that will do it for you, and various scanner options.
You could do this.
Epson makes great photo scanners. I assume you are scanning 35mm? Slide film has to be back-lit to scan, so conventional scanners won’t work. If you are going to do it yourself, Epson’s flatbed beat everything else in a casual user’s price range. This is the cheapest one that does film: https://www.bhphotovideo.com/c/product/887065-REG/Epson_b11b207221_Perfection_V370_Scanner.html
They get nicer from there. If you need larger formats you need a V550, V600, or V800 depending on budget and format.The ones with large transparency support can be retrofit with, say, a 3D printed slide film frame for specialty formats.
If you have only a few, and still need this I have an Epson V500 that has the backlight and holders for 2x2 slides, 35 mm and Medium (2-1/4 x 2 1/4) film strip at high resolution (2000 dpi - slowly) on down.