While it's not possible to switch a video in an existing campaign, you can reallocate those funds to start a new campaign with a new video.
Please note before proceeding:
You may be required to deposit additional funds to start the new campaign. This requirement is waived if you've spent less than 25% of your original campaign's budget (<$12.50 on a $50 campaign) or if Google Ads did not approve your video.
TO USE THE FUNDS FOR A NEW VIDEO/CAMPAIGN:
1. Click the gear icon next to the campaign containing the funds.
2. Click the "end campaign" (trash can) icon.
3. When prompted, click "End Campaign" in the window displayed. Wait 5 minutes for the funds to return to your account wallet.
4. Create a new campaign and set the budget to match the funds in your account wallet. Upon submitting the campaign, the funds in the wallet will automatically apply.