Stuck trying to fill cells in PowerQuery

I am fairly new to PowerQuery and still learning.   I have a query that is very close to what I need (this file is made smaller for clarity withy rows and columns removed)

For Members with a single line entry, there is no problem as this is what I need - e.g lines 266 and 647 and others lower down

The problem is for members with multiple roles where they do training course when in a specific role - e.g. Member 811 (Helen) who has eight separate roles.   I cannot seem to work out how to do the following

• For Courses 1 to 4 (and other columns like them) where there is a single date entry in all the roles (rows), or multiple identical date entries, I need to fill the other blank cells in that column with the same date already in that column.
• For Courses 5 and 6, I need to populate any blanks with the most recent date, leaving the others as they are

I'm sure it must be 'obvious' to experienced users, but I am stuck......and very frustrated.

I do hope someone can help - thanks in advance !!