What statistical test to use to say frequency of one sample is higher/lower than the frequencies in other samples? I have the following table,

I used chi square test of independence to find whether the frequencies of 'c.388A>G' are same across SAMPLE_A, SAMPLE_B and SAMPLE_C. And the p-value from the test shows that they are not the same. Now , I want to make a statement that "The frequency of c.388A>G was significantly higher in SAMPLE_C compared to other groups that had similar but lower frequency." But to say that, should I do any other test? If yes, can you please advise what test I should do?

I think the simplest is to run a t-test to show that the frequency of sample_c is higher than sample_2 and then another test to show that it is higher than sample_1 and you can divide the p-value by 2 (bonferroni correction) or some other multiple hypothesis testing scheme.
There are other tests. You can take the maximum frequency between sample_A and sample_B (0.49). Then calculate a p-value by calculating the probability, using a binomial distribution, of getting 0.61 or higher and use the total number of samples in sample_C. This is called a binomial test.
