How can I fix the heavy whipping cream? I whipped it, left to tend to something and came back to re-whip and it turned to liquid.

for some reason the link didn't stick:

I read something way back when that suggested adding a bit of gelatin to the cream as you whip it, to hold it together - mine often separates a bit if I whip it ahead of time, even in the frig. This is roughly what I do but I use less gelatin if I don't need the whipped cream as a "frosting" but just a dollop on top of a dessert.

I agree with the above. Depending on how stiff you whipped it to begin with, it very well could have broken down in that amount of time. I have problems with that, too. It will re-whip but may not hold very long the second time around.

You may have over-whipped it, and the liquid you see could be what's left after the cream has given up its butter. If that's the case, drain it through some cheesecloth add a little salt to the butter and enjoy it. Then start over with a new batch of cream.

Chill the cream and when it's cold try whipping it again