Having preeclampsia once what to do to prevent this again? My babies died after 20 days in icu bec they were premature 28 weeks

Aspirin! I am very sorry for your losses. Aspirin 80-81 mg daily would be my recommendation unless you are allergic or have gastritis or peptic ulcer disease. Take it before getting pregnant for maximal prophylaxis benefit: can be 15-75% decrease in risk of recurrent preeclampsia. Take calcium as well if you are lactose intolerant otherwise dairy product consumption suffices. Do not change sexual partners.
Early intervention. I am so sorry for your loss. Preeclampsia is an awful disease that can have very dire consequences. Fortunately, there are ways to monitor your pregnancy so that signs and symptoms are recognized early to allow early interventions that can help make for a safer pregnancy and healthy outcome. Make sure to discuss your experience with your doctor. Stay in close contact and alert her to any concerns.