Learn Hardcore Ukrainian: Гарантійний ремонт зроблять безкоштовно. - The warranty repair will be done free of charge.

gender: <a class="border-b border-dotted border-blue-400 dark:border-blue-500 cursor-pointer text-inherit no-underline" href="/grammar/ukrainian/nouns/gender/overview">masculine
number: singular
case: <a class="border-b border-dotted border-blue-400 dark:border-blue-500 cursor-pointer text-inherit no-underline" href="/grammar/ukrainian/cases/accusative/forms">accusative singular

Literally, it means they will do/make. But in sentences like this, Ukrainian often uses they with an unspecified human subject. So the sentence does not mean that some specific group called they is important. It means something like:

They will do the warranty repair for free
or more naturally in English, The warranty repair will be done for free

The implied people are the workers, technicians, or service center staff.

Why does Ukrainian say зроблять ремонт instead of using a verb meaning repair directly?

In Ukrainian, зробити ремонт is a very common expression. It literally looks like do/make a repair, but it is a normal way to say carry out a repair.

So:

зробити ремонт = to do/carry out a repair
ремонтувати = to repair
відремонтувати = to repair/fix completely

All of these can work in different contexts, but зробити ремонт is very natural and common.

Why is ремонт in the form ремонт, not some different ending?