Place this code in page settings → Custom code → Footer section, replace the BLOCKID with your block name, save and preview
<script>
window.addEventListener('block-loaded-BLOCKID', () => {
setTimeout(()=>{
[...document.querySelectorAll('#BLOCKID .form-input-label')].forEach((label)=>{
if(label.innerText == "Old password"){
label.innerText = "TRANSLATION FOR OLD PASSWORD"
}
if(label.innerText == "New password"){
label.innerText = "TRANSLATION FOR NEW PASSWORD"
}
})
}, 100);
});
</script>