I'm looking for some advice on calculating individual theta scores for 900 people who've responded to a healthcare questionnaire, as part of a factor analysis/multidimensional item response theory analysis I'm trying to carry out - if anyone can help me?

We've run rotated (promax oblique) factor analyses, and found 2 factors, each that load ~10 questions well.
I've run the multidimensional IRT for each of the factors, and have results on discrimination and item difficulty, and looking now to calculate each individual participants' total theta score for each factor. We have individuals' total numerical score (for the questions that correspond to each factor), but I'm not sure how to calculate each persons theta score?

If anyone has any suggestions, would be really appreciated. Thanks for your thought!