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I meen 7S3P - 7X3.7=25.9V

For Lithium Ion = LiIon cells
Vmax = 4.1V or 4.2V fully charged
Vmin = ~= 3.0C. Slightly lower is possible but there is almost no energy left and you risk cell damage.

7 x 3.0V = 21V min.
7 x 4.2 = 29.4V max.
So IF you charge 7 cells in series you need about 30V DC.
IF you want to charge 3P strings at full capacity you need 3 x 2A = 6A.
You can charge slower.
Your 24V supply is not high enough to charge all 7S cells directly.
You need a boost converte or a higher voltage supply.

21 cells requires about 21 x 2A x 4.2V max ~= 180 Watts - although less can be OK.
Your 24C, 6A supply can provide 24 x 6 = 144 Watts.
If you use a boost converter to 30V if overall efficiency is 80% then you need 180/80% = 225 Watts OR your 14 Watt supply at 24V will deliver 144 x 80% = 115 Watts at 30V.
115W into 7S3P at 4.2V cell = 115/21/4.2 = 1.3A = 65% of maximum allowed. This is acceptable - charging will take less than 50% more time than best allowable.

But you still require a charge controller IC. .

Q&A:

So its meen that I can charge my 3S3P battery pack with 24v max 6AH Charger?

A cell requires up to 2A x 4.2V = 8.4W.
Your charger is rated at 24 x 6 A = 288 Watt.
So using a boost or buck converter that will charge about 288/8.4 =~ 288/9 = 30+ cells. BUT you will need to use a converter to do this.
If you connect to battery with a linear requlator you have 6A max or up to 3 strings in parallel and not more than 5S so 5 x 3 = 15 cells max. .

3S3P = 9 cells.
You say 21 cells.
Do you means 3S7P = 21 cells?

BUT
3S = 14.6V max, 9V min. 4S = 16.8V - 12V
5S = 21V - 15V
6S = 25.2V - 18V
7S = 29.4V - 21V

A 24 VDC charger will charge up to 5S without a boost converter.

If you want 24V nominal you need 6S or 7S or maybe 5S.
How do you intend to do speed control?

What IC or controller do you intend to use?
Just connecting 24 V to cells will not work - as I think and hope you know. .
You need a specialist LiIon charger IC. Digikey sells a number that would be suitable.