Add columns from existing table in PowerPivot O365

[Mason391]

I have some fairly complex PowerPivot reports that were initially created in an older version of excel. In that version you could easily add columns and remove columns from a database table by checking or unchecking a box, I believe under design>edit table. Under the new O365 that functionality has been removed. I go to design>table properties and from what I have found so far it only shows fields I've already brought in , then I go to design then have to run a sequel script and it doesn't allow editing?? I need to add in columns from a table into the powerpivot and can't seem to figure it out. I can pull in all fields through a new connection but then I loose all my dax formulas and relationships to other tables etc... I've been googling to no avail. Help!!