How do I fix missed spots, dimples or low spots in a cured flood coat?

The only seamless fix is to re-coat the whole surface. You can't fill just the low areas: UltraClear Bar & Table Top Epoxy has to self-level to 1/8" thick, so it can't be thinned or brushed on thinner, there's no runnier version for syringe touch-ups, and UltraClear Deep Pour Epoxy won't work (it's only for voids 1/4" or deeper).

To re-coat: 1. If the last pour is 4 to 10 hours old, no prep is needed; the layers bond as one. 2. Past 10 hours (it's sandable after 12), lightly scuff the entire surface with 220 or 320 grit sandpaper. Don't sand through to the wood; if you do, re-seal it first or the new pour will bubble. 3. Wipe off all dust with a clean, lint-free rag and denatured alcohol or acetone, never paint thinner or mineral spirits. 4. Pour a fresh flood coat over the whole top, pouring each batch within 20 minutes of the last so they flow together.

The sanding scratches disappear under the new coat and it cures clear.

To spot-fix instead, scuff just the bare or low spots with 220 to 320 grit, clean with acetone, then brush on or pour a small amount of epoxy, smoothing brush strokes with a heat gun. Deeper dimples may need several brush coats 4 to 6 hours apart. Expect seams where new epoxy meets old; on some projects they barely show, on others they do. Cutting out and re-pouring a section won't look seamless either.