join in
US /dʒɔɪn ɪn/
UK /dʒɔɪn ɪn/

1.
mitmachen, teilnehmen
participate or become involved in an activity with others
:
•
Everyone was singing, so I decided to join in.
Alle sangen, also beschloss ich, mitzumachen.
•
Don't be shy, just join in the game!
Sei nicht schüchtern, mach einfach mit beim Spiel!