Summary: Gender-selection methods which involve astrology should be avoided (as astrology is forbidden). An Islam Q&A fatwa considers natural methods (such as adjusting one's diet) as permissible. However, it's doubtful that any of these actually work. IVF-based gender selection was considered permissible in a SeekersHub fatwa, but the attitude was "superior to simply leave such matters in the hands of God".
... I can search on internet and found some method can increasing possibilities of baby boy, like , Women diet ( Alkaline food ) plan, her period time calculation, male diet plan, position of intercose ( sex ), time of intercourse ( sex ) and moon night calculation.
It's probably safe to say all of these are pseudoscience and old wives' tales. (I asked about this here Is pseudoscience generally forbidden or discouraged? but it's yet to be answered.)
There's some scientific papers on the topic, e.g. Mathews et al., You are what your mother eats, 2008 (PubMed), which reported "Fifty six per cent of women in the highest third of preconceptional energy intake bore boys, compared with 45% in the lowest third." From the point of view of someone wanting to influence their offspring's sex, this is a very minimal effect. Moreover, the underlying claim is strongly contested:
We examined the hypothesis using new evidence from the wartime famine in Holland in 1944-1945 and failed to show an association between maternal diet in pregnancy and the sex ratio. This makes a causal link highly improbable.
Cramer and Lumey, Maternal preconception diet and the sex ratio, 2010 (PubMed)
(See also Young et al., Cereal-induced gender selection? Most likely a multiple testing false positive, 2009 (PubMed).)
There is a risk, therefore, that this behavior is putting belief in superstitions, which Islam is against in general; see What does Islam say about superstitions? In fact, "Moon night calculation" sounds like a form of astrology, and astrology is definitely forbidden (IslamWeb).
However, Islam Q&A regard natural methods as permissible:
It is permissible to choose the gender of the foetus by natural means, such as following a certain nutrition plan, chemical washes, and choosing times for intercourse according to the time of ovulation, because these are permissible means and there are no reservations about them.
Islam Q&A say that means beyond this are not permissible:
It is not permissible to use any kind of medical intervention to choose the gender of the foetus, except in cases of medical necessity ...
There are methods of gender selection (such as IVF), and a SeekersHub fatwa described this as permissible according to the resolution passed by the Majma al-Fiqh al-Islami in 2007. Based on Qur'an 42:49 (He creates what he wills. He gives to whom He wills female [children], and He gives to whom He wills males), the fatwa goes on to say:
While choosing the gender of a child is not necessarily being discontent with divine decree, it is superior to simply leave such matters in the hands of God.