If statment between 2 dimensions table

Hi,

I want to create a dax column with something like that :

If  Table1[ColumnA] = "Something",

Then Table2[ColumnB],

Else Table1[ColumnA]

Table1 and 2 aren't related and can't be related. There are also 2 table between these.

There are in a schema like this :

Because my tables aren't related, I can't use a simple related fonction.
Someone have an idea how to solve it ?

Thanks !