Sucks for you that the software does not prefill the dividends. I’d suggest you look them up here: ICTax - Income & Capital Taxes
Note the “Basel-Country: reduced tax value”-flag that I guess you should check? I honestly have never seen that before but it reduces the taxable value.
I suggest you click “Show details” and enter the number of shares you had at 31.12.2020 in the “Nominal quantity”-field. If you need to know how many shares you had when I would generate the “Activity Report” for 2020 (might take a while, you can download it asynchronously).
There you see when you traded VT, your year opening and year closing balance (I think). Otherwise reverse-engineer it via your trades and the year-end position.
Then use those numbers on ICTax in “Details of the calculation” to enter at what dividend-distribution date you had what amount of shares. This will determine the taxable income.
Then enter those four dividend-distributions (if you held for the whole year) in your software (tick “mehrere Coupontermine”.
I interpret your input-fields like this:
“Anzahl per Termin” = number of shares at that dividend-distribution date
“Fälligkeitstermin” = date of the distribution
“steuerbar /Stk. in CHF” = dividend per share in CHF (row “Value per share CHF” on ICTax)
“stb. Gesamtertrag in CHF” = “anzahl per termin” * “steuerbar /Stk in CHF”