I want to make longer pregnancies and I saw that you need to end all town pregnancies but I don’t know do that.

One way is to use Master Controller to terminate each pregnancy. The command is under MC > (Sim) > Advanced > Pregnancy. (MC Cheats module required)

Another way is to let each pregnancy come to full term and allow the babies to be born, without allowing any new pregnancies to form in the meantime if you have that level of control over your world. Or you could use CmarNYC's Pregnancy Controller mod to put each currently pregnant sim into labor right away.

You can trigger labor with DebugEnabler as well.