• ket the sun shine in,
• pet the sun shine in,
• oet the sun shine in,
• lwt the sun shine in,
• lst the sun shine in,
• ldt the sun shine in,
• lrt the sun shine in,
• l4t the sun shine in,
• l3t the sun shine in,
• ler the sun shine in,
• lef the sun shine in,
• leg the sun shine in,
• ley the sun shine in,
• le6 the sun shine in,
• le5 the sun shine in,
• let rhe sun shine in,
• let fhe sun shine in,
• let ghe sun shine in,
• let yhe sun shine in,
• let 6he sun shine in

The adverb for the phrase "let the sun shine in" would depend on how you want to modify the action. Adverbs typically describe verbs, adjectives, or other adverbs. For example, if you want to describe how the sun shines in, you could use adverbs like brightly, warmly, or brilliantly. If you want to describe how the action of letting the sun shine in is "done, you could use adverbs like gently, eagerly, or quickly".