Sinned Knowingly

Can a person do teshuva for a sin they committed knowingly and willfully thinking 'I will do teshuva later after I have sinned'
This is something that has been troubling someone very close to me and is preventing them from moving forward as they feel they will never be forgiven and they feel that they cannot do teshuva because they will probably commit the sin again.
Please answer quickly and delicately if possible because I want to be able to show them this post as an answer.
I am trying to give them proper chizuk and any advice would be helpful.
Thank you so much.

Rambam Teshuvah 4:6

ו כל אלו הדברים וכיוצא בהן אף על פי שמעכבין את התשובה אין מונעין אותה אלא אם עשה אדם תשובה מהן הרי זה בעל תשובה ויש לו חלק לעולם הבא.

 

All these sins listed that are obstacles to teshuvah, dont prevent teshuvah from being accepted. Including sinning intending to do teshuvah afterwards. The Rambam specifies that for such a mindset, Hashem doesnt assist the person in doing teshuvah. I saw that this is becuase this mindset takes teshuvah lightly. I assume the first step would be to realize why this mindset is wrong.

That said, the short answer is yes, a person can do teshuva even though he intended to do so beforehand. 

 

But now, he has one more thing to do teshuva for.

 

At the end of the day, אין לך דבר העומד בפני התשובה. It's just that sometimes Hashem allows us an easy time to do Teshuva, and sometimes we don't merit such help.