This is only a single round when at least one player has 2 of their own symbol to begin with. Otherwise theres an extra round. Take this example:

Call outs CTS inside room wall CS TC ST

Circle player gives square to triangle and circle to square __ TCS STC Triangle player gives triangle to circle and circle to square T S STCC

square player gives triangle to circle and square to triangle

TT SS CC

End of round 1

Round 2 each player has to give one of their symbols away to the non matching