Becoming a Muslim is an easy and simple process. All that a person has to do is to say is the Testimony of Faith (Shahada), which is pronounced as :

ムスリムになるには、ひとつのシンプルで簡単な手順を踏むだけです。つまり必要なことは、信仰証言（シャハーダ）と呼ばれるフレーズを口にすることだけです。

لَااِلَهَ اِلَّا الله مُحَمَّدٌ رَّسُولُ الله
I testify : La ilaha illallahu Muhammadur-rasulullah

These Arabic words mean, “There is no true god (deity) but God (Allah), and Muhammad is the Messenger (Prophet) of God.”

私は「ラー・イラーハ・イッラッラー、ムハンマドッラスールッラー」と証言します。
そのアラビア語の意味は、「神（アッラー）以外に真の神はなく、ムハンマドは神の使徒（預言者）である」というものです。

To be a Muslim, one should also :

🌙 Believe that the Noble Quran is the Book of God
🌙 Believe in the Prophets and the Books He revealed
🌙 Believe in His Angels
🌙 Believe that the Judgment Day (Resurrection Day) is true and will come
🌙 Not worship anything nor anyone except God
🌙 Accept Islam as his/her religion

The conversion/revert can be done alone, but it is much better to do it with the help of a Muslim (for example : an Imam of a masjid) so they could help you to pronounce the sentence right and provide support to get started the newfound faith. InshaAllah.
Alternatively, if you need further assistance, you may drop us message at anytime.

[Congratulations on your Shahadah]