If you use the domains.lt name servers and want to change DNS records, you have to log onto the self-service, select the menu item “Data management” and click the link of the domain which DNS records you want to change. Click the link “Manage the domain’s DNS records” in the opened window.
More information on the authorised types of the DNS records is available at https://domains.lt/en/faq/for-technical-representatives-contacts/what-is-dns-and-what-type-of-dns-records-are-authorised-by-domains-lt/
If you are using the name servers other than domains.lt, you cannot change DNS records in the self-service of the domains.lt. The registrar whose name servers you are using has to provide you with the information on how to change DNS records.