I remember a story about Spike going to Africa, doing the trials but, instead of getting his soul, he's allowed to go back in time to season6 and fix things for Buffy and for them together. But I can't find it. I don't remember the title either. Can someone help me?

Hi g0tik4_,

I'll keep looking but right now it makes me think of three stories.
P-S to S6 time travel fics: Hero's Reward by pfeifferpack
Summary: Setting: Begins post AtS «Not Fade Away» and rapidly goes to S6.
Given a chance to do things differently a hero finds that putting another first and ignoring his own desires can lead to his rewards beyond his hopes.

and Before He Screwed It Up by Hello_Spikey.
Summary: Spike inadvertently makes a wish to «go back before he screwed it all up» --sending Angel Season 5 Spike back to the morning after Buffy Season Six Spike first gets it on with Buffy.
Can he use his knowledge of the future to fix things? In the world at large, sure, but particularly his relationship with Buffy? He'll find it's easier said than done.

The third one is Pandora's Boxer by speakr2customrs

Summary: At the completion of his trials in Africa, Spike is offered an alternative to a soul; a second chance. The cave demon sends him back in time 3 years — but wipes his memory of the intervening time! Will the same things happen all over again — or will it work out a little differently? Could this be a second chance not only for Spike, but for Buffy and the Scooby Gang? In a world in which «Kick the Spike» is a game more dangerous than juggling with nitro-glycerine, can they learn to respect the vampire and avoid the mistakes they made first time round? Or will entirely new mistakes lead them to a different but equally catastrophic destination?

Edit: Found two more. Time travel from the trials.
Here Is Gone by Terri Botta and here. 
Summary: Spike gets a chance to do a few things over again.

Anticipation by 2writers4spike EF, ff.net, The Bloodshedverse.

Summary: Having no idea how it happened, Spike finds himself back in 1977, reeling from a newly acquired soul and more guilt than most could handle. After dodging Drusilla, his main focus is getting back to his own time and back to Buffy in Sunnydale so that he can atone for all he's done. That is, until he sees the newly born slayer in 1981 and goes off in a new direction. Can he stop the events that brought misery to Buffy's life, or will he be forced to watch destiny destroy the woman he loves all over again? 2writers4spike is the penname used for collaborations between dawnofme and mabel marsters

Thank you, it was actually Hero's Reward. I thought it was after Africa, but it was after NFA.