What exactly did you tighten? The crank bolt that fastens the crank to the axle?
Or, the bottom bracket itself?
Is the crank loose, or is it the bottom bracket?
Isolate the exact problem first before proceeding.
Did you remove the crank and tighten the bottom bracket?
If you attempted to tighten the bottom bracket (BB) and it is still loose and noisy, it needs to be replaced.
Plan on spending about $40 for a replacement.
If, you tried to tighten the crank with the single crank bolt, and it is still loose, the inner faces are probably worn so they are no longer square. The crank therefore needs to be replaced.
An experienced mechanic can certainly help you diagnose the problem and offer you advice.