Aside from the fact that neither of those cards support SLI in the first place, in order to use SLI, you would need two identical cards. Im not super familiar with SLI, but it might even get as specific as needing two of the same brand/model cards, not just two of the same GPUs. Now, SLI is different from having two GPUs in the same system. You can have both a 2060 and 3060 running in the same computer, but there is no reason if you have one monitor, at all. if you have two monitors, then the GPUs will only power the monitor they are connected to. This also has very limited usefulness, and may only help by a percent or two, if it does at all.
TL: DR It wont work, if you already have both GPUs, build a second PC, or sell the extra GPU.