These two trips overlap. You can either change their dates or assign each overlapping day to one trip so it only counts for that trip.
Overlap: —
1) Change the overlapped dates
Edit start or end date of either trip so they no longer overlap.
2) Leave dates as they are — assign each overlapping day
Assign each overlapping day to one of the two trips. Helpful if you were transiting between two places on the same day, or if you just went somewhere for a getaway or quick visa run.
3) Make one a sub-trip of the other
Nest one trip inside the other (e.g. a day trip during a longer stay). The overlapping days will count for the sub-trip and the icon turns gray.