Welcome, @Jritchie70! You may want to introduce yourself in the welcome thread!
Only enter it once and do NOT force the Dexcom to match your hand meter. Your hand meter is only accurate to +/- 20% or so. Your Dexcom is averaging numbers over time, and is doing a better job than any single number out of your hand meter. So it is almost always better to let the Dex do the averaging.
It happens, in particular when the Dex sensor fiber has moved, that your Dexcom ends up way off, maybe 30 mg/dl or more off. In that case, you are better off hand metering twice and entering both calibrations over 5-10 minutes, once after the other, rather than double entering one value.
Do note, btw, that the Dex only averages when your hand meter value is ABOVE the Dex. If it is under, the Dex will go to your value or very close to it.
Also note that the number displayed by the Dex right after you enter your hand meter number is NOT the number that it will eventually display on your track, it is an intermediate value with no practical signficance.