I figured it out myself. Here's the code.
console.log('waiting for iframe with form to be ready.');
await page.waitForSelector('iframe');
console.log('iframe is ready. Loading iframe content');
const elementHandle = await page.$(
'iframe[src="https://example.com"]',
);
const frame = await elementHandle.contentFrame();
console.log('filling form in iframe');
await frame.type('#Name', 'Bob', { delay: 100 });