Help i am trying to do something but it wont work

https://musescore.org/en/handbook/3/voices

Not sure what your problem is:
- First write the upper line as voice 1 (d, c-sharp, d, c-natural);
- Then select "voice 2" ...
- ... and write all the sixteenths (semiquavers). You'll see some really shocking effects, e.g. when c and c# are put near to each other shortly before you raise the c to a c#, whence the two noteheads nicely collapse into one - but it worked like a charm for me.

H.M.