The fixture numbers of your fixtures are displayed in the "Ch #" column.
Any fixture's number can be changed, so that the fixture can be controlled by a different fader/fixture number in syntax.
To change the channel number of a single fixture, tap on the channel number cell, and type a new fixture number. On FLX, this can be any number between 1-9999, on FLX S24 this is between 1-48, and on FLX S48 this is between 1-96. After changing the fixture number, that fixture can now be controlled using the new channel fader number.
To renumber multiple fixtures at the same time, select the fixtures in the order you wish them to be numbered. Then select the column header button which is labelled “Ch #”. This will open an onscreen number pad. When you edit this value, the fixtures selected will be renumbered sequentially in the order they were selected and shown – they won’t all be given the same channel number.
It is recommended that you take some time thinking about numbering your fixtures. For example, it is common to ensure your fixtures are sequential, from stage right to stage left, which won't necessarily be the order of DMX addresses.
On FLX, it is common to start each different type of fixture on a new hundred. For example, dimmers start from 1, LEDs start from 101, first type of movers from 201, next type of movers from 301 etc.
If you have fixtures such as MAC 700's, you might want to number these starting at 701 onwards, as a very quick way to remember which number they are.
On Solution consoles, the channel faders are numbered 1 - 48 (or 1 - 96 on the Solution XL). Fixtures can also however be assigned to the MFKs. These are numbered 101 - 300.