Thanks to the detailed step-by-step procedure, you will be able to do it step by step. Read the procedure in case you are:
If you are a volunteer and have worked at least 40 volunteer hours in the previous year, you can donate up to 3% of your tax.
If you are a legal entity, you can also donate 2%, 1% or less to more than one beneficiary, subject to a minimum donation of 8 Euro.
All the necessary forms for remitting part of the tax can be found at this link.