If you have a single mother or father, click/tap on the child and click/tap "Add father" or "Add mother" and it'll add another parent, though it may not be partnered correctly with the other parent. You can also click/tap on the parent and click/tap
"Add partner/ex," though you'll have to click/tap on the child and pick the mother/father from a list on the from family tree button.
If you simply have a child without parents, such as the first person added, you can click/tap "Add parents"
Both of these are done on a person's desc./profile.
If you have a different situation than these, explain and I'll try to answer it.
