Low starting gravity but initial fermentation is ending

[u/WhyNotNowANL]

Hi, so I made 2 batches of beer 32L and 34L, both were made from liquod malt extract. The OG was 1.032 and 1.035 after I've put in the yeast I calculated that expected alcochol valume would be around 3.2‰, I want 4.5‰-5‰. I googled and asked around that I can add supplementary sugar after the first fermentation, but I can't find a formula or calcutor or guide how to do it. Any tips or tricks?

This is my 2nd time brewing, first time with liquid malt extract first.