The earliest text here reads in the indicative as “if thou wilt”. In the 1837 edition, the wilt was replaced by will, giving the subjunctive “if thou will”. This secondary form was maintained until the 1874 RLDS edition and the 1879 LDS edition. The critical text will maintain the earliest reading, wilt, although both wilt and will are theoretically possible here. For further discussion of this choice, see under Alma 8:20.
Summary: Maintain in Helaman 9:20 the indicative form wilt in “if thou wilt”, the reading in 𝓟 (the earliest extant source).