When copying from 𝓞 to 𝓟, Oliver Cowdery initially wrote the past participle forgotten as forgot, the simple past-tense form of the verb forget. In this instance, Oliver is responsible for the change, but he later caught his error and corrected forgot to the standard forgotten. The correction is supralinear and is written with a sharper quill, and the ink flow is darker. Perhaps Oliver made his correction when he was proofing 𝓟 against 𝓞. Or maybe his change represents later editing that just happens to agree with 𝓞. In either case, 𝓞 reads forgotten.
Usually the text has forgotten for the past participle (ten times), but in Alma 60:20 there are three occurrences where the simple past-tense form forgat (soon altered to forgot) was used as the past participial form instead of the standard forgotten. For discussion, see Alma 60:20 as well as past participle in volume 3.
Summary: Based on the earliest textual sources, the standard past participle forgotten in 1 Nephi 7:11 should be maintained.