The Qualified Lawyers Transfer Scheme (QLTS) covers lawyers from a wide range of common law and civil law jurisdictions.
To be eligible to apply for admission as a solicitor, you must be a qualified lawyer from a recognised jurisdiction. Find out if your jurisdiction is on the list of recognised jurisdictions of the SRA. A qualified lawyer is a lawyer whose qualification gives the lawyer rights of audience, makes the lawyer an officer of the court in that jurisdiction is awarded as a result of a generalist (non-specialist) legal education and training, was not gained via a shortened or fast-track route to qualification, and has been gained in a recognised jurisdiction.
Note that there are no formal requirements you need to comply with before you can take the QLTS assessments. You can simply contact the assessment provider and register to sit the assessments.
The requirements as explained above should be met when you apply for admission as an English solicitor, not as a pre-requisite to take the QLTS assessments