Question

voice change of -I didn't know anyone else was here.

Answer 1

hey mate here is ur ans

when it is past tense in active voice we use was /were +3rd form of verb in passive voice

so we can turn the above from active to passive as follows

It was not known by me that anyone else was here.

hope it helps you
have a great day ahead

Answer 2

HEY MATE

IT WAS NOT KNOWN BY ME THAT ANYONE ELSE IS HERE.

hope it helps you