First you need to understand in what areas you want a mentor and what are your expectations.

You may be a engineer, you might want to grow in your domain, or switch to a different role like product or manager. So you need to understand in what areas you want to be mentored and as a the next step you need you figure out whom to reach out to. Filter out the people you have been inspired by, it can be in your workplace or outside in forums like linkedin or someone whom you feel comfortable with, you need not have to right away choose them. If you many options you can try to set 1:1's with each of them and understand who would suit you best.

Keep in mind you can change your mentors after some time, when you feel like you have learnt their skills and you right away know what would be their approach or answer before you reach out to them.