Test with Saved Primers can only be used on sequences that are annotated as oligos - these are denoted by the green arrow icon in the Document Table. If you have primer sequences stored as DNA sequence, you can convert them to oligos using the “Convert to Oligo” function under the Primers menu and they should then show up when you run Test with Saved Primers.
Also Geneious may not be able to find the oligos in your database while the indexer is running or paused. Check down the bottom left of the screen under the Sources panel to see if this is the case. If the indexer is paused, click on it to restart it, allow it to complete and then your oligos should show up again. See also “Why is my indexer continually running?” under the Databases section.