Choose impedance value of ferrite beads at any frequency
Smps works with 2.5 Mhz. What should be impedance value. How can I
chose this value ?

You probably won't find many ferrite beads that operate effectively at 2.5 MHz. They are usually targeting above 30 MHz. The one below is good from about 30 MHz to 500 MHz for example: -

In some applications the one above might only be useful between 60 MHz and 200 MHz. It depends entirely on what you are trying to achieve.
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This article is very useful if you want to know about ferrite beads.
If you are trying to reduce the ripple voltage from your SMPS it's probably better to use an inductor and capacitor filter.