Click on Settings:
Find Object Manager:
In Object Manager, you need to repeat the steps below for Lead / Contact / Account / Opportunity…
Open the object to modify and click fields and relationships:
Under Data Type, choose formula and move forward.
Give a name in field tag and field name.
Under formula return type, click text and continue.
On the next screen, click Insert field and choose the fields to be concatenated by adding " & " between them.
In this example:
DDD _ Test _ _ C and Phone _ Test _ _ c
Then continue and choose the profiles to take safely from the field and continue.
Now simply click Save and Create.