How to combine the data of all subdomains for each domain?

Question

Google Analytics

Has a standard output format source / referrals:
site1.com 10
m.site1.com 5
en.site1.com 20
br.site2.com 13
lt.site2.com 5

What do I need?
site1.com 35
sitre2.com 18

As I understand it, in Google Analytics this can only be done crookedly, and irreversible functions like a filter with a regular expression + a replace function .... I
went to Google Data Studio , but I still don’t understand how to create my own "parameter" and possibly "indicator"? The bottom line, I think it is clear what needs to be achieved from the example above, so that the data would be without division into subdomains, but as a single domain, but would read data from its domain and all its subdomains.
Thanks in advance if anyone can advise.
//Ps: solution options pointwise for 1 site are not relevant for me.