How should robots.txt be edited when redesigning a site?

Question

Search Engine Optimization

The website has been redesigned. Some links have changed. And some remained the same, but the content and appearance of the page itself were updated on them.
These sections remained in the Bitrix admin panel. In the sense of the old version of the site and the new one.
Moreover, in addition to our site, we often make other sites with a third-level domain, such as test.mainsite.ru.
for our tests.
How should the robots.txt file be edited in this case?
And is such a site organization bad at all? Or is it necessary to take everything to hell and not post anything besides the main site?

Answer 1

Well, there are a lot of things here. Did the structure stay the same during the redesign or did it change? If the structure has changed, then you need to map the old links to the new ones (here excel will do), then set up redirects from the old addresses to the new ones.
Regarding subdomains, why would you index your tests at all? Close them in robots and don't spoil your search results.