Torah repair involves taking a Torah which is not kosher, and turning it back into a kosher Torah. Depending what is wrong with the Torah, this can be a short process or a long process.
Some Torahs need just a little bit of work to turn them into perfectly good, kosher Torahs.
Some Torahs can be made kosher quite easily, but not necessarily beautiful.
Some Torahs can be made to look beautiful, but to make them actually kosher is a lot more work.
The sofer will usually spend an hour or two looking through the scroll so as to get an idea of what sort of work the Torah needs. Depending what they find, they may discuss different options with you. Then they will leave you with an estimate and you can decide how you would like to proceed.
Repair, like writing, must be done by someone who is kosher to write for your community. Therefore, if your Torah scroll is, or is likely to be, used by a non-egalitarian community, I will not repair it.