I think i understand him ...
I suppose u just registered the domain on dot.tk w/o registering account there , so the NS changing may be hard
u need to make account there , then attach ur .tk domains .
When logging to ur .tk domain panel u need to browse "Set Name Servers" on control panel , i repeat not on web000 panel but on .tk panel and set the NS to:
on domain u wana point to web000.
After that ur domain gona start pointing to 000webhost panel in maximum 72hours.