How can I search for a particular inflected form of a word while keeping the main Search tab?

Select the word, and right-click on it to open the contextual menu. Then select Search For > Inflected. Accordance will look for this form in the same text in another tab (placing it in quotes).

You can find the selected inflected form in another text, if you press the option or alt key as you amplify from your selection to the new text.