Don't think about more. It's easy to way follow the way.
Go to your Fiverr inbox.
Select the Conversation:
Find the conversation with the buyer for whom you want to send a custom offer.
Click on "Offer Custom Order":
Within the conversation, you should see an option to "Offer Custom Order" or something similar. Click on it.
Fill in the Details:
Fill in the details of the custom offer, including the service you are providing, the delivery time, the price, and any additional terms.
Send the Custom Offer:
Once you've filled in the necessary details, send the custom offer to the buyer.
Wait for Acceptance:
The buyer will receive your custom offer and can choose to accept, decline, or request modifications.