Hi,
The general rule is that the relief is available for the tax year in which the shares are issued or, where you have invested in an approved knowledge intensive investment fund, the year in which the fund closed. But, if you choose, you can treat some or all of the shares as issued in the previous year and claim relief in that previous year, subject to the maximum limit for the year. You will find the date of issue of your shares recorded on form EIS3 and the date the approved fund closed on form EIS5. You can see guidance here:
HS341 Enterprise Investment Scheme — Income Tax relief (2023)
Thank you.