If the XSLT uses few XSLT 2.0 and XSLT 3.0 advances, and you are a sophisticated XSLT developer, then work your way through
and adapt each in-play XSLT 2.0 and 3.0 concept and construct back to XSLT 1.0. There is no automated conversion solution, and this is not a task suitable for a developer unfamiliar with XSLT.
Otherwise, your options include:
- Use a more modern framework that supports modern tools, or
- Find a way to incorporate an XSLT 3.0 processor into your framework. (Consider Saxonica's products, which support a plethora of platforms), or
- Apply the XSLT 2.0/3.0 transformation in another stage of your pipeline outside of the weak tool that only supports ancient XSLT 1.0.