'Messages'→ tap the 3 vertically stacked dots→'Trash'→tap & hold the texts or conversations you want to restore (you may see 'Select conversations')→'Restore' Alternately: tap on the conversation→'Edit'→whioe in 'Select messages' you can choose 1 or multiple (by tapping the circle(s) to the left of it/them to select) or can just select 'All' (by tapping the circle right above it to select that)→'Restore'
If they're not there, then you may be able to restore them via Samsung Backup, but it'll restore all texts that were present at the time the backup took place. If the texts in question weren't there yet or were already gone by the time the backup took place, then it won't be able to retrieve those specific texts along with all of the others that were backed up.
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