In the 1Password app, use 1Password - New vault on this PC.
Configure the vault to your liking and use Choose a folder to sync this vault to select the destination of the local database.
In RDM, create a new 1Password entry. Set the Mode to Linked to a local file.
Use the ellipsis button to select the local database file. Its extension will beopvault and it will be located in the folder you selected earlier.
Once that is done, all there is left to do is to select which credential you wish to retrieve, using the Title field or its ellipsis button If you’d rather not select a credential and be prompted with every use instead, check Always prompt with list instead.