1. Check the easy places first

Ask the sender to send it again, if it was sent to you recently.
Gallery trash: if you deleted it from the gallery, look in "Recently deleted".
WhatsApp backup: if you have a Google Drive backup from before the deletion, reinstalling WhatsApp and restoring it brings old media back. This replaces newer chats, so think before you do it.

2. Scan the phone

WhatsApp saves media in its own folders and keeps thumbnails. Deeps Recovery searches there too:

Allow All files access.
Choose Videos or Photos. Each type has its own scan.
Run a Deep scan: it also checks app caches, thumbnail stores and hidden folders (see Quick, Deep or Full Scan).
Results are grouped by folder; open the WhatsApp folders and preview the files.
Select them and tap restore.

Start as soon as possible. Every new photo or video can overwrite deleted files. Sometimes only a smaller thumbnail can be found.

Lost WhatsApp voice notes instead? See Recover Deleted WhatsApp Voice Notes.