without an event for a radiobutton or checkbox, how can I set it true or false programmatically

I have a page with radiobuttons and checkboxes; the form has previously been filled out by the user. I need to bring the form back up for them to edit the EXISTING data, which means I have to programmatically check checkboxes and check radio buttons.

If I HAD an event, I could easily change the corresponding control with srcElement, but there is no event in this case. I haven't been able to find a way with document.getElementById('XXX'). ??? to work in any way.

Using Angular 4 if that helps.

Thoughts?

Thanks in advance, :-)