useRef

import React, { useRef } from 'react'

export default function TextInputWithFocusButton() {
    const inputEl = useRef(null)
    const handleClick = () => {
        inputEl.current.focus()
    }

    return (
        <>
            <input ref={inputEl} />
            <button onClick={handleClick}>Focus the input</button>
        </>
    )
}

<script>
	let inputEl

	function handleClick() {
		inputEl.focus()
	}
</script>

<input bind:this={inputEl} />
<button on:click={handleClick}>Focus the input</button>