Conditional Column Power Query (M): how to repeat the value for some rows and then change the value

Hi everyone,

i'm trying to achieve the follow in power query:

here's what i have as native database 

 and this is what i wolud like:

so basically take one value from first column and repeat for some amout of rows.

I was trying with index and referst to previuos row but of course this won't work.

Do you think it is possible to achive this?

Does anyone has some hints on how to do it?

Thanks in advance!