@Pedro250
Forget what PokeChu said. Because of the way assigning of a worldmap works in Fire Red, it's not possible to assign only Sevii Island Nine's world map value to the first World Map and not all the values in between 0x8E (Power Plant, the latest value of Worldmap1) and 0x9E (Sevii Island Nine's value). You will need to rearrange more than one worldmap value to get it the way you like.
Which worldmap loads is dependent on the worldmap value of the current map you're on. The game determines which of the four worldmaps should load in the following manner:
Every worldmap value below the value at 0x0C0064 (0x8E in Vanilla Fire Red) will automatically be assigned to the first worldmap (Kanto in vanilla Fire Red). For the worldmap values past 0x8E, the game determines which worldmap loads by checking a table starting at 0x3F1AA4. If a worldmap value should be assigned to the second worldmap, it should be written before the first 0xC5 value in the list. If a worldmap value should be assigned to the third worldmap, it should be written before the second 0xC5 value in the list. If a worldmap value should be assigned to the fourth worldmap, it should be written before the third 0xC5 value in the list. If a worldmap value is above 0x8E (in Vanilla Fire Red) and is not in the table somewhere, the game will not know which worldmap to open. In that case the worldmap will appear glitchy.
For a more extensive explanation I refer to the tutorial I sent earlier.
Also, if you're using a hex editor: make sure to use Paste Write, not Paste Insert. That will make the ROM file bigger which will lead to a white screen.
