By deceasing the value of pH

In water Cu(I) disproportionates to Cu(II) and Cu(0), The latter one precipitates out, you can't stabilize Cu(0). Instead. add a ligand, such as neocuproine, to stabilize Cu(I). pH adjustment would not work, see the Pouarbaix diagram for Cu.

Dear Hossein Zamani

This seemingly simple question is not that easy to answer. It depends on what you want, what is the 'starting' situation, do you need water or a buffered system, etc. See for excellent answers the following related question here on RG: https://www.researchgate.net/post/Why-CuII-is-more-stable-than-CuI

Best regards.

Yurii V Geletii Thank you very much. This short tip helped me a lot

Rob Keller Thanks for the link you gave me

Perhaps you want to check:

https://www.researchgate.net/post/How_to_concentrated_a_CuI_chloride_solution_in_ammonia_can_be

Carlos Araújo Queiroz thanks dear carlos