The standard answer is too combine your Likert-scored items into a scale that you would then use as a moderating variable (i.e., it would interact with the independent variable to produce different effects on the dependent variable.

Because there have been so many questions here about Likert-scored items, I have compiled a set of resources on this topic:

https://www.researchgate.net/post/How_can_one_help_people_create_simple_scales_from_Likert-scored_items

The Likert scale can be used on the items defining the moderating variable, as is done for the independent and dependent variables.

that's certainly possible. As David mentioned, you want to combine your items into a sclae and then use this scale as a continuous moderator (if combining the items makes sense conceptually and the items are homogeneous).

Implementation of the moderation analysis in SPSS and SAS  is pretty straightforward with Andrew Hayes's PROCES macro (see also here: http://afhayes.com/introduction-to-mediation-moderation-and-conditional-process-analysis.html)

thank you so much for all the answers! i really appreciate it!