Forecast forward using observed data

Hi, please see attached spreadsheet.

The deseasonalised month and day are combined to create the combined view of that day.

I have 731 days historical data.

I would like to be able to forecast forward (eg: what will happen on day 732 or 780 for example).

Can you explain what I need to do? I have been looking up LOGEST, Forecast, Trend etc but not sure where to start!!

Many thanks for your help.