Help predicting values based on historical data

Hi,

New poster looking for some help.

I have a large range of data from various companies with various properties. I'd like to be able to predict future sales based on historical from previous quarters.
I have tried the FORECAST function however as I understand it, it requires a value to base off, i don't have a future value as I'm looking for an estimate based off the previous data.

I have tried to use the Forecast sheet but it didn't seem to want to play nicely with the Quarterly dates, and I don't know how to work out any seasonal variation.

Attached is a sample of the data I am looking for, I have left the spaces I would like it to predict as empty cells. I am open to any solution except VBA as this is for someone who is not partically excel savvy.

Any help would be greatly appreciated and if you require further info please let me know.