扌 is the hand radical 手 in left-side form. It marks 捂 as a hand action, alongside 打 (hit), 拉 (pull), and 推 (push) - here the action of pressing a palm over something to cover it.
吾 supplies the reading, shifting tone from wú to wǔ. The same phonetic surfaces in 悟 (realize) and 晤 (meet face to face), all clustered around the wu syllable family.
