Open Snapchat and check the Chat screen
Tap the conversation with the person you want to review
Scroll through the chat if messages are still available
Check saved messages marked in chat
Look for messages in Memories if they were saved there
Check your device notifications for message previews
Request your Snapchat data from the Accounts portal
Download the data file after Snapchat sends it
Open the downloaded file and review chat history if included
Check if the other person still has the messages
Restore from a phone backup if your device backup contains the chat data
Contact Snapchat Support if you need help with account or data access