SQL Server allows you to automatically recycle error logs and this is great because it gives you more of a hands-off approach. However, if you require to do it manually, you can use the stored procedure sp_cycle_errorlog as shown below.
Once you execute the following T-SQL script, it creates a new error log file and start recording latest entries into it.
Similarly, the following script recycles the SQL Server agent error log file.
USE msdb ;
EXEC dbo.sp_cycle_agent_errorlog ;
If you are looking to manage SQL Server logs effectively, refer to the article - https://www.sqlshack.com/how-to-manage-sql-server-logs-effectively/